Flexible cutting tool and methods for its use

ABSTRACT

A cable comprising helically wound superelastic fibers and having a drilling tip provided at its distal end is housed in an elongated holder through which the cable may be advanced, the holder having a distal end for supporting the cable during a drilling operation and through which the distal end of the cable may protrude. The holder includes contains a cable support shaped to bend the cable through a predetermined angle adjacent its distal end and to support the cable as it is rotated and advanced. A motor is attached to the cable remote from the distal end of the cable to rotate the cable in a direction tending to tighten the cable fibers.

FIELD OF THE INVENTION

The invention relates to flexible cutting tools and to surgical drillingand other cutting procedures using such tools.

BACKGROUND OF THE INVENTION

Modem surgical techniques often require holes or channels to be cut intobone, teeth or soft tissue, for various reasons. Holes may be drilled inbone to receive screws, sutures or bone anchors enabling anchorage ofimplants or reattachment of ligaments or tendons. Ordinarily, surgicaldrills can be employed which utilize a motor (often an air motor) and adrill bit of the desired length and diameter. However, because of theproximity of other tissue or prosthetic materials, it often becomesdifficult to appropriately orient a surgical drill and drill bit so thatthe desired bore can be formed in tissue. Dental drills are available,of course, but have generally very short bit lengths.

U.S. Pat. No. 5,330,468 (Burkhart) proposes a drill mechanism forarthroscopic surgery in which a rotating pin of nitinol is caused toemerge from a gently bent aiming tube, drill through a thickness ofbone, and then be received in an appropriately positioned receivingtube. The device itself is somewhat bulky. Another device using nitinolpins or probes is shown in U.S. Pat. No. 4,926,860 (Stice et at.). Here,a needle or other probe of nitinol may be received in a curved cannulato deliver the end of the probe to the desired location. The probe isthen advanced through the cannula and exits from the cannula end in astraight orientation.

If a nitinol pin, as shown in the previously mentioned U.S. Pat. No.5,330,468, is bent through a sharp angle and rotated at high speed, thepin becomes work hardened at the area of the bend due to its constantflexing during rotation. The superelastic characteristic of the pin inthat area is reduced, and the pin can readily break. Nitinol wire drillsin which a nitinol pin is rapidly rotated in a sharp bend, hence, havenot become commercially successful.

SUMMARY OF THE INVENTION

We have found that an appropriate flexible cutting instrument can beformed through the use of a helically wound cable, preferably of metaland most preferably of nitinol or other superelastic alloy. Cables ofthis type can withstand rapid rotation while proceeding about tightbends, without substantial work hardening. Because cables are far moreflexible than solid pins of the same diameter, it would be expected thatthe distal free end (that is, the cutting end) of a cable, since it isrelatively unsupported, would tend to whip around in an uncontrolledfashion. That is, a trade-off to using a much more flexible superelasticalloy cable would be lack of control of its drilling end.

We have found that the cutting end of a flexible cable that is slidinglysupported in a stationary tubular support from which the cutting end mayprotrude, when used as a drill, produces a bore that remains relativelystraight and true as the cable is advanced, even though the cable lengththat protrudes from the tube is supported only by the tissue beingdrilled. As long as the cutting end remains in contact within the tissuebeing drilled, the tissue itself appears to provide sufficient supportand guidance to the otherwise unsupported cutting end to keep it in asubstantially straight path.

As used herein, "tissue" refers to both soft tissue and to hard tissuesuch as bones and teeth.

Thus, in one embodiment, the invention relates to a cutting instrumentsuch as a drill that includes an elongated, helically wound flexiblecable preferably comprising superelastic metal alloy fibers and cuttingmeans disposed at the distal end of the cable to perform a drillingfunction when the cable is rotated. A motor attached to the cable remotefrom its distal end rotates the cable in a direction tending to tightenthe helically wound fibers. That is, if the cable is given a clockwisespin, the cable should have a counter-clockwise wind. Provided also isan elongated holder having an opening through which the cable may beadvanced axially, the holder having a distal end for supporting thecable during a drilling operation and through which the distal end ofthe cable protrudes. The holder includes a cable support shaped to bendthe cable through a predetermined angle adjacent its distal end and tomaintain that bend as the cable is rotated and advanced in a drillingoperation. In a preferred embodiment, the helically wound superelasticalloy fibers themselves are cut at the distal end so as to themselvesform said cutting means. This cable is preferably so formed as to enablefibers at the distal end of the cable to separate from each otherslightly under centrifugal force or axial compression or both as thecable is advanced through the holder and rotated; as a result, thediameter of the drilled hole is slightly greater than the diameter ofthe cable adjacent but spaced from its distal end. Axial compression ofthe cable end against the floor of the bore causes the individual fibersof the cable to bow outwardly and thus increase the diameter of thecable at that point.

The invention includes a method of drilling straight holes throughtissue which comprises providing the drill referred to above, rotatingthe cable in a direction tending to tighten the helically wound fiberswhile continuously maintaining the cutting means at least partiallywithin the hole being drilled and advancing the cable through theholder, whereby the wall of the hole being drilled serves to support thecutting means so that the latter advances in a substantially straightpath through the tissue.

A particularly preferred procedure involves a method for fastening ahollow intramedullary rod to a bone, such as the femur, within which therod is received. Rods of this type may be employed to internallystabilize fractures of long bones such as the femur, the tibia and thehumerus. The method includes the steps of providing a drill including anelongated, flexible length of superelastic alloy bearing cutting meansat its distal end and an elongated holder receivable in the hollowintramedullary rod. In this embodiment, the length of superelastic alloypreferably is in the form of a cable as described above. The holder hasa distal end for supporting the length of superelastic alloy during adrilling operation and an opening through which the distal end of thelength of superelastic alloy protrudes. The holder includes a supportshaped to bend the length of superelastic alloy through approximately aright angle adjacent its distal end and to maintain the bend during adrilling operation. In this procedure, the holder is positioned in theintramedullary rod, the hole through which the distal end of thesuperelastic alloy cable length protrudes being aligned with andreferencing a preformed hole in the intramedullary rod. The length ofsuperelastic alloy is then rotated in a drilling operation and isadvanced radially outwardly from the holder through the aligned holes inthe holder and rod, against and through the bone and against and throughthe overlying muscular tissue and skin while continuously maintainingthe cutting means at least partially within the hole being drilled. Thepoint of exit of the drill from the skin is located, and a cannula isinserted over the cable to engage the hole through the bone. The cannulais stabilized with respect to the bone, the cable is retracted, and adrill is employed to enlarge the hole, the drill extending through theopposed wall of the bone. A screw fastener is inserted through thelateral hole thus drilled in the bone and through the preformed hole inthe intramedullary rod to hold these elements together.

Other surgical uses of the instruments of the invention include dentalprocedures such as root canal surgery, the cleaning of osteolyticlesions resulting in bone cavities adjacent a prosthesis, the repair ofanterior cruciate ligament damage, and the like.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a broken-away, perspective view of a drill of the invention;

FIG. 1A is a detailed view of the distal end of the drill of FIG. 1;

FIG. 2 is a broken-away, schematic view of a cutting tip of a drill ofthe invention shown forming a bore in bone;

FIG. 3 is a schematic, broken away diagram of a leg with a broken femur,the latter being internally stabilized by placement of an intramedullaryrod; and

FIG. 4 is a broken-away, schematic view of a device of the invention asthe same is used in connection with the intramedullary rod shown in FIG.3.

FIG. 5 is a broken away, cross-sectional view of a device similar tothat of FIGS. 1 and 2, suitable for use in connection with theintramedullary rod shown in FIG. 3;

FIGS. 6A and 6B are broken away, cross-sectional views of a portion ofthe device shown in FIG. 5;

FIG. 7 is an exploded view, in partial cross-section, of a device forinserting a connector in an intramedullary rod of the type shown in FIG.3;

FIG. 8 is a broken away, cross-sectional view of a simplified device ofthe invention showing particular details, and FIG. 8A shows a specificcutting end;

FIGS. 9A, 9B and 9C are broken away, cross-sectional views of an endportion of a device of the invention showing a method of angleadjustment;

FIG. 10A, FIG. 10B and FIG. 10C are broken away, cross-sectional viewshowing a modified embodiment of the invention; and

FIG. 11 is an end view of a device of the invention of the type shown inFIGS. 10A, 10B and 10C, illustrating a modification of the device.

DETAILED DESCRIPTION

A flexible cutting tool of the invention, exemplified as a drill, isshown as 10 in FIG. 1. A flexible, helically wound cable is showngenerally at 12, the cable extending through the interior of anelongated tubular support 13 that itself is supported by an elongatedtubuIar holder 14. Support 13 closely receives the cable and supportsthe cable against undue lateral movement or buckling even when the cableis rotated rapidly or is under torsional or axial load. The innerdiameter of the tubular support 13 preferably is no more than twice thediameter of the cable, and in general, the inner diameter of the tubularsupport need be only about 0.001 to 0.005 inches larger than thediameter of the cable. At its distal end 16, the tubular support 13 isbent through an angle so that its inner surface 18 serves as asupporting surface to support the cable as it bends through apredetermined angle to exit from the side of the holder 14. In FIG. 1,the cable 12 is bent through approximately 90°. Distal end 20 of thecable protrudes from the distal end 22 of the tubular support 13.

A motor 26 is shown in FIG. 1 for rotating the cable 12 about its axis.The motor can be any rotating driver, and may take the form of anelectric motor or an air motor, the latter being driven by compressedair entering the motor through supply tube 28. Although the motor may berotated at whatever speed is desired, speeds of about 50,000 rpm areappropriate. For certain uses as described in greater detail below,slower speeds are required. Rotational speeds can be varied from a fewrevolutions per minute up to 150,000 revolutions per minute or more. Themotor 26 may be mounted to the proximal end of the cable 12 usingcommonly available chucking equipment, crimping techniques, or adhesivebonding. It is contemplated that the cable 12 may run through the motor26 with the rotating portion of the motor engaging the outer walls ofthe cable in a manner enabling the rotating cable to be advanced axiallywith respect to the motor. Preferably, however, a chucking arrangementis employed in which the proximal end of the cable 12 is received in thechuck of the motor in known fashion, that is, using the chuckingmechanism that is common to power drills and drill bits. With thispreferred embodiment, the motor 26 is fastened to the cable 12 so thataxial movement of the motor and cable distally toward the distal end ofthe holder will cause the end 20 of the cable to advance outwardly ofthe hole 22 for at least a distance equal to the depth of the desiredhole. In one embodiment, the motor 26 may be mounted to the proximal end30 of the holder, and the holder itself, rather than being formed from asingle tubular member as shown in FIG. 1, may be formed of two or moretubular members that telescope together such that the length of theholder 14 can be lengthened or shortened. In this embodiment, shorteningthe length of the holder 14 causes the cable 12 to advance distally outof the hole 22. The telescoping portions of the handle 14 may, in fact,have mating circumferential threads such that rotation of one portion ofthe handle with respect to the other through a given angle will resultin a predetermined advancement of the distal end 20 of the cableoutwardly of the hole 22.

The distal end 20 of the cable is shown best in FIG. 2. The cable,preferably of nitinol or other superelastic alloy, desirably is formedabout a central core wire 32 about which are twisted a plurality ofstrands as shown in the drawing. Any twisted cable of the type depictedwill operate, such as cables having successive layers of oppositelytwisted fibers, as long as the outer layer of fibers is twisted in adirection causing the fibers to wrap more tightly as the cable isrotated. Preferably, the cable contain only a single layer of twistedfibers, the twist direction being the same for each fiber.

From FIG. 2, it will be seen that if the cable is rotated in thedirection shown by the arrow A, the helically wound strands will tend totighten upon one another, torque thus being readily transmitted from themotor to the distal end 20 of the cable. It will also be understood thatif the cable is rotated by the motor 26 in the opposite direction, thecable will tend to untwist and become quite loose. Rotation in thedirection of the arrow A in connection with the twist direction shown inFIG. 2 thus is important to proper operation of the drill. It shouldalso be understood that in FIG. 2, the distal end portion of the tubularsupport has been omitted to enable the twisted nature of the cable to bebetter illustrated. In practice, the cable is supported by the tubularsupport throughout substantially the entire length of the cable exceptfor the distal end portion that is received and supported in the tissuebeing drilled.

At its distal end, the twisted fibers forming the cable may tend toseparate from one another slightly under the substantial centrifugalforces generated by the motor 26 or from axial compression of the fibersagainst the floor of the hole or both. FIG. 2 shows the twisted strandsseparating slightly as the drill is used to form a bore 34 in a bonemass B. Note that the diameter of the bore 34 is somewhat larger thanthe diameter of the cable 12 spaced away from the end 20 of the cable.Here, the cable strands 33 have separated and have spread outwardlyslightly so that the bore 34 is slightly larger than the cable diameter.Some clearance thus is provided between the inner surface of the boreand the cable itself, and this is believed to help in preventing bindingof the cable within the bore and to permit debris from the drillingoperation to escape. As the rotational speed of the cable is increased,the separation of strands at the distal end of the cable increases undercentrifugal force; hence, one may control the diameter of the borethrough adjustment in rotational speed of the cable.

At the distal cutting edge of the twisted fibers, it should be notedthat the fibers are maintained within the previous diameter of the holeand are supported by that diameter as they cut. In this manner, the holeor bore 34 itself serves as a support or guide that prevents the distalend of the cable from moving in an uncontrolled manner and which causesthe bore 34 to remain straight. Soft tissue provides similar support.

The support 13 in the embodiment shown in FIG. 1 is tubular with acentral lumen 15 housing the cable and being only slightly larger thanthe cable 12, as discussed above, so as to permit the cable to rotatesubstantially freely in the holder while preventing the cable as itrotates from kinking or doubling back on itself. The distal end of theholder of FIG. 1 is itself bent through a predetermined angle,exemplified as an angle of 90 degrees, the surface of the lumen at thebend furnishing the support that serves to maintain the 90 degree bendof the cable as the latter rotates and advances through the holder.Various other configurations supporting the cable at its bend can beemployed. For example, the holder may simply be provided with an orificeat or adjacent its distal end through which the cable may be advanced,and the inner surface of the holder may be smoothly curved to supportand maintain the bend in the cable. The holder may include an elongatedgroove, formed in an insert in the holder if desired, that houses andsupports the cable for at least a portion of its length. If desired, thelumen 15 may be provided with constrictions spaced along its length, theconstrictions providing supporting surfaces positioned to contact andsupport the cable at one or more points along its length.

In the drawings, the tubular support 13 and holder 14 are shown asdefining a mechanically separate device which can be received within ahollow intramedullary rod or the like. In an alternative embodiment, anintramedullary rod or the like may itself define the support. Forexample, generally solid intramedullary rods are known in the art. Suchan otherwise solid rod can be provided with art internal passage whichis sized and shaped much as is the support 13 described above. In suchan embodiment (not illustrated in the drawings), the intramedullary rodperforms the functions of the holder 14 of the invention and the passagein the rod performs substantially the same function as the supportdetailed above.

Any suitable cutting tip can be used at the end of the cable 12. In oneembodiment, when the cable is rotated and thus forming a bore largerthan the diameter of the cable adjacent the loop. Also, if a loopcutting end is used, the loop may be used to pull a suture through theformed bore when the cable is withdrawn from the bore, thus simplifyingsurgical procedures involving fastening ligaments or tendons orcartilage to bone.

As noted above, the end of the cable can simply be cut straight acrossat a right angle to the length of the cable. The resulting sharp ends ofthe individual fibers thus cooperate to form the drilling tip. Ifdesired, the fibers at the distal end of the cable may be weldedtogether to prevent them from separating under centrifugal force. Also,a separate drill bit similar to drill bits currently in use for surgicalprocedures can be used, the drill bit being welded, crimped, glued orotherwise fastened to the distal end of the cable. In one embodiment,the drill bit may have cutting edges at its distal end but may includean axial bore formed in its proximal end sized to receive the distal endof the cable which can then be welded into the drill bit bore. Ofcourse, whenever a separate drill bit is attached to the end of a cable,there is some risk that the drill bit may come loose during a drillingoperation. As a result, it is preferred that the drill bit be formed bythe ends of the strands forming the cable, as shown in FIG. 2.

The use of a highly flexible cable of the type described above in adrilling procedure also offers the advantage that the cable will follow,in a drilling operation, the softer part of material being cut. Forexample, root canal surgery commonly requires that a hole be drilledthrough the root of a tooth following the nerve canal. The nerve canalof a tooth is slightly curved. Dental drills currently in use arecomparatively rigid and cannot, accordingly, easily follow thedeviations from straightness that are common to root canals. However,the cutting tool of the present invention, which makes use of a veryflexible cable, is capable of being inserted into the root canal of atooth and, by being gently advanced, can perform the desired cleaningand nerve removal by following the normal canal curvature. Moreover,since the depth of the hole that is drilled is dependent upon thedistance in which the cable is advanced through the opening in thehandle, the end of the handle can be rested upon the surface of thetooth being drilled, and the depth of the bore in the tooth can becontrolled with great accuracy. Further, since the fibers at the end ofthe cable can be caused to flare outwardly (see FIG. 2), the flaredfibers can be employed in a procedure to cut, dislodge and displacematerial beyond the ends of the roots, a procedure that is difficultwhen using present day dental instruments.

The present invention provides, in a preferred embodiment, a methodenabling accurate intramedullary rod placement and securement to a bone.With reference to FIG. 3, the femur F of a patient is schematicallyshown as having several fractures, the bone segments being internallystabilized by means of an inserted intramedullary rod 40 having a hollowinterior 42 and a series of preformed holes 44, 46 formed through itswalls. The purpose of these holes is to receive bone screws that aredriven from the exterior of the leg inwardly through the bone wall tosecure the bone to the rod.

Proper location of the holes in the intramedullary rod has been aproblem. One method involves using a fluoroscope to locate the holes inthe rod, and then place Stimen pins or the like percutaneously throughthe femur and the corresponding holes in the rod, using the pins asguides in the subsequent placement of screws. An inherent hazard of thisprocedure is exposure of the patient and medical staff to gammaradiation. External targeting of the rod holes without use offluoroscopy but using instead knowledge of the hole locations withreference to the proximal (exposed) end of the rod is difficult becausethe rod often must bend and twist as it is impacted into theintramedullary canal of the bone. Screws that are not properly placedneed to be removed and replaced, leaving an additional hole in the boneand requiring additional operating time.

According to one embodiment of the invention, this problem is approachedfrom a different direction. Once the hollow intramedullary rod has beenimpacted into place in the bone, as shown in FIG. 4, a drill 50 of theinvention having an appropriately slender shape is inserted into the rodfrom its proximal end and is advanced until the distal end 52 of thecable, bent through 90 degrees as shown in the drawing, can be extendedthrough a hole 44 in the rod. The motor is activated and the cable isadvanced axially to cause a hole to be drilled radially outwardlythrough the femur. The drilling operation can be continued through softtissue exterior to the femur and can, if desired, be brought outwardlyof the skin, all as is described in greater detail below in connectionwith FIGS. 5-7.

The invention has been described above primarily with respect to thesuperelastic alloy nitinol, but other superelastic materials may also beused, as well as such other materials and metals such as stainlesssteel. Nitinol is a superelastic (sometimes referred to aspseudoelastic) material, that is, a material that can be processed ortreated to exhibit superelasticity at a desired temperature such as bodytemperature. A number of shape memory alloys are known to exhibit thesuperelastic/pseudoelastic recovery characteristic, and these aregenerally characterized by their ability, at room or body temperature,to be deformed from an austenitic crystal structure to astressed-induced martensitic structure, returning to the austeniticstate when the stress is removed. The alternate crystal structures givethe alloy superelastic or pseudoelastic properties.

A modified device of the invention is shown in FIGS. 5 and 6 as 60. Ahandle grip 62 is provided with a bore 64 within which is telescopicallyreceived a tubular housing 66. An elastically compressible helicalspring 68 is positioned between opposing shoulders of the handle gripand tubular housing as shown in the drawing. Finger grip 70 is providedto enable the device to be conveniently grasped in the hand such thatwhen the finger grip 70 and handle grip 62 are squeezed towards oneanother, the tubular housing 66 extends more deeply into the bore 64 tocause a cable to protrude from the instrument. At its proximal end, thetubular housing has an expanded portion 74 which houses the impeller 76of a simple air motor which is driven from an air source (not shown) andwhich is capable of developing substantial rotational speeds. Speeds onthe order of 40,000-50,000 RPM are appropriate for many drillingfunctions, although speeds of rotation can be varied as desired.

Extending within the bore of the tubular housing 66 is an elongatedtubular support 78 having a curved distal end 80. Extending through thetubular support is a cable 82 of the type described above sheathedthroughout the majority of its length in a drive tube, the proximal endof which is axially received in and clamped in the impeller 76 as shownin the drawing. The distal end of the cable extends beyond the distalend of the drive tube and through the bend 80 of the tubular support. Itwill be understood that as the finger hole 70 and handle grip 62 aresqueezed together, the cable 82 is caused to extend further from thecurved section 80.

The handle grip 62, and its distal end, includes an elongated tube 84terminating in opposite, outwardly extending bosses 86, 88, the bossesbeing so shaped as to enter the holes 44 formed in an intramedullary rodof the type shown in FIGS. 3 and 4. Boss 88 has a hole formed through itas shown best in FIG. 6B to receive the curved end 80 of the tubularsupport 78. The bosses 86 are formed on distally extending, generallyparallel arms having upstanding pins 90 formed on them. A camming block92 is provided with angled slots 94 within which the pins 90 arereceived, the slots being configured such that when the camming block ismoved distally, the pins 90 and hence the bosses 86, 88 are movedtogether to enable the device to be removed from an intramedullary rod.On the other hand, when the cam block 92 is moved in the proximaldirection, the bosses are forced away from each other and into opposingholes formed in the intramedullary rod to anchor the end of the toolappropriately in the rod. A wire 91 extends from the camming block to afinger grip 72 slidably mounted at 93 to the handle grip. As the fingergrip 72 is moved toward the handle grip 70, the bosses 86, 88 are causedto separate to the position shown in FIG. 5. Movement of the finger grip72 in the opposite direction causes the bosses to retract toward eachother.

Referring again to FIG. 5, the handle grip 62 includes an obliquechannel 96 for fluid delivery for lubrication, irrigation or cooling,the channel having an appropriate external fitting such as a Luerfitting 98.

With reference, then, to the procedure described above in connectionwith FIGS. 3 and 4, it will be understood that the tube 84 of the handlegrip 62 is sufficiently long as to extend the length of anintramedullary rod. The tube 84, with the bosses held in their retractedposition by the cam block 92, is inserted into the intramedullary roduntil the bosses 86, 88 are adjacent to the holes 44 in the rod. Oncethe bosses have entered the holes (as can readily be sensed by thesurgeon), the cam block 92 is moved proximally to lock the bosses in theopposing holes in the intramedullary rod. The air motor is energized,and the cable is advanced in a drilling operation as has been describedearlier.

FIG. 7 depicts apparatus which can be used to place a bone screw orother connector through the bone and intramedullary rod shown in FIG. 3.As noted above, the cable 82, after drilling through the wall of thefemur, will continue to drill in a substantially straight path throughsoft tissues of the thigh and will emerge from the skin. Shown in FIG. 7is a hollow introducer rod 100 within which is received a cable clamp,the latter comprising a rod 102 received within a tubular housing 104.At its bottom end, the tubular housing 104 includes an internal rubberseal 108 to receive the end of the cable and to clamp onto the cable asthe rod 102 is moved axially within the tube 104. The end of the cableprotruding from the patient's skin is captured within the rubber seal108 so that the cable may be firmly supported. The introducer rod 100 isthen slid axially downwardly along the cable clamp and the cable whileholding the cable in tension until the conical end 106 of the introducerrod is received in the rim of the hole in the femur through which thecable protrudes. The introducer rod is held firmly against the rim ofthe hole, and the cable clamp is then removed. The cable itself can bewithdrawn from within the introducer rod, and the entire apparatus shownin FIG. 5 can be set aside. Over the introducer rod is then advanced aguide tube 110 carrying within it a drill sleeve 109. The guide tube 110has a convenient handle 112 to aid the surgeon in supporting theinstrument. At its distal end, the drill sleeve 108 has bone seatingspikes 114 which are driven into the surface of the femur around thehole that had been drilled, following which the introducer rod isremoved. At this point, a long surgical drill is inserted through thehollow center of the drill sleeve, and a hole of greater diameter isdrilled through the femur, the drill bit passing through theintramedullary rod and thence through the opposite side of the femur.The drill and supporting drill sleeve are then removed, and a fixationscrew (not shown) can be advanced through the guide tube 110 andfastened through the holes drilled in the femur and through thepreformed holes in the intramedullary rod to firmly attach together thefemur and the intramedullary rod.

FIG. 8 is a broken away, largely schematic view showing details of thedistal end of a device of the invention. A length of cable as describedabove is shown at 120, the cable and drive tube 125 (described below)slidingly being received in a tubular support 122. The tubular supportis in turn axially constrained within a tubular housing 124. As shown,the cable is sheathed in a drive tube 125 which extends from a point 127spaced from the distal end of the cable proximally into mountingengagement with the impeller. The drive tube is secured to the cable bycrimping at either or both ends, by the use of an adhesive, or by othersimilar means. As the air motor is moved distally, that is, to the leftin FIG. 8, the cable 120 is advanced outwardly of the tubular support122.

Note that the distal end of the tubular housing 124 includes asupporting element 130 having a proximal portion 132 that is receivedwithin the end of the tubular housing 124 and a nose 134 extendingapproximately at right angles to the housing 124. Supporting element 130is formed with a curved bore within which is seated the distal end 136of the tubular support 122, the supporting element 130 holding thetubular support 122 and distal end 136 rigidly so as to properly guidethe cable 120 as it emerges from the tubular support. The nose 134 maybe made as narrow and tapered as desired to enable it to fit, forexample, accurately against the surface of a tooth above the root, theinstrument being appropriate for use now in performing a root canalsurgical procedure.

The cable may be bent adjacent to its distal end through anypredetermined angle ranging from 0 degrees to 180 degrees. Moreover, theelongated tubular support holder through which the cable is passed andtrained about the predetermined angle may itself be adjusted before orduring use. FIGS. 9A, 9B and 9C show a cable 140 carried by tubularsupport 142 within an elastically bendable tubular housing 144, thelatter, if desired, being made from nitinol or other superelastic alloy.The tubular support 142 is provided with a series of spaced notches 146cut into one side wall adjacent the distal end of the support. A controlwire 148 extends within the tubular housing 144 adjacent the tubularsupport 142, the wire being attached to the tubular support at 150 onthe same side of the tubular support as are formed the notches 146. Aswill now be noted from FIGS. 9A, 9B and 9C, as the wire 148 is pulledproximally, the walls of the notches 146 tend to pinch together andpermit the tubular support 142 to bend. This, in turn, also tends tobend the distal end of the tubular housing 144, all as illustrated inthe drawing.

FIGS. 10A, 10B and 10C illustrate another way in which a predeterminedangle may be set at the distal end of a device of the invention. InFIGS. 10A, 10B and 10C, an elongated tubular support holder 160 is shownemerging from a tubular housing 162. The tubular support may be bent asdesired as shown in 10B, and the cable 164, which is slidably receivedin the tubular support 160, can then be extended from the end of thetubular support. The tubular support 160 may, if desired, be bentmanually by the surgeon so as to enable the distal end 166 of thesupport to be appropriately placed adjacent a bone or other tissue to bedrilled. Alternatively, the tubular support may be of superelastic alloyhaving the preformed shape shown in FIG. 10C, the flexible nature of thesupport 160 enabling it to be housed in a generally straightconfiguration within the tubular housing 162 as shown in FIG. 10A and toprotrude in a curved fashion when advanced distally within the housing162, the curved nature of the support 160 enabling it to be steered asdesired.

As will be appreciated from the foregoing description, the apparatusesof the invention may be employed for a variety of purposes. Oneapplication involves anterior cruciate ligament reconstruction. In thisprocedure, a ligament graft, either a separate graft or a section of thepatellar ligament, is passed through a hole prepared in the tibialplateau. Proper placement of the exit site of the hole in the tibialplateau is critical to long term functioning of the graft and of theknee. If the hole is placed too far anteriorly, the graft will impingein the femoral notch, resulting in early failure. If the hole is placedtoo far posteriorly, the graft will not provide the needed stability tothe knee.

Using conventional techniques, the distal hole in the tibia to acceptthe graft is drilled from an exterior anteriodistal approach. With thepresent invention, however, a surgeon is able to start the drillingprocess from within the joint space, directly targeting the desired borelocation with the drill. The cable is advanced distally and emerges fromthe tibial anterior cortex distal to the joint. A cannulated drill isthen advanced over the cable and into the joint space, exiting at theappropriate point on the tibial plateau. The same technique may be usedto prepare the femoral drill hole from the intracondylar notch. Thus, bystarting the drilling operation from inside the joint space, accuratelocation of the bore is made possible.

Osteolysis, the formation of a lesion in bone around an implant, maylead to substantial damage to the bone. Osteolytic lesions are commonlyprogressive, leading to loose and painful implants, fracture ofsupporting bones, or failure of the implant. Revision surgery is oftenthe only available option to treat such lesions. However, theflexibility of operation that is afforded by cutting instruments of theinvention may enable lesions to be cleaned and filled without extensivesurgery. Once a portal is drilled through the cortical bone surroundingthe lesion, a cutting instrument of the type shown in FIGS. 10A, 10B and10C may be advanced into the lesion cavity. As the cable is advancedinto the lesion, it may be carefully controlled so as to drill awaysmall portions of the commonly much softer lesion material. However, ifa substantial length of cable is permitted to protrude from theelongated cable holder tubular support, the end of the cable may bepermitted to randomly tumble about the lesion cavity, selectivelycleaning away the soft lesion material.

Referring now to FIG. 11, a cutting instrument of the invention, astypified in FIGS. 10A, 10B and 10C, can be equipped with various otherelongated instruments for performing different functions. FIG. 11 showsthe end of an instrument of the invention. Here, an outer tubularhousing is shown at 170, the housing carrying within it a cable 172 andtubular cable support 174. Also carried within the housing 170 may be anoptical fiber bundle 176, and small tubes 178, 180 which may be employedto flush the cutting site with water or other cleaning liquid. Thisconstruction lends itself to the cleansing of osteolytic lesions asdescribed above. The optical fiber bundle 176 permits the position ofthe cable to be continuously visualized as cleaning of the cavityoccurs, and the tubes 178, 180 may be employed to flush away theliberated lesion material. Particularly when the end of the cable ispermitted to move randomly, the strands at the end of the cable may beunwound slightly to permit the strands to open up, or the wires of whichserve to cut away the lesion material. Once the lesion is cleaned out,the lesion cavity may be filled with bone cement or with bone graftmaterial. The use of bone graft material supports reformation of thebone in the lesion cavity, whereas bone cement would inhibit debris frominfiltrating the space and triggering another osteolytic lesion. Inconnection with the osteolysis procedure described above, since the endof the cable may be permitted to whip about randomly in the bony cavitythat is being cleaned, the speed of rotation should, of course, be farless than the speed of rotation when the instrument is being used as adrill.

While a preferred embodiment of the present invention has beendescribed, it should be understood that various changes, adaptations andmodifications may be made without departing from the spirit of theinvention and the scope of the appended claims.

We claim:
 1. Method for drilling a hole through animal tissuecomprisingproviding a drill including an elongated, flexible cablecomprising helically wound fibers and bearing cutting means at itsdistal end and an elongated holder having an opening through which thecable may be advanced axially, the holder having a distal end forsupporting the cable during a drilling operation and through which thedistal end of the cable protrudes, the holder including a cable supportshaped to bend the cable through a predetermined angle adjacent itsdistal end and to maintain such bend as the cable is rotated andadvanced distally, rotating said cable in a direction tending to tightenthe helically wound fibers while continuously maintaining the cuttingmeans at least partially within the hole being drilled, whereby the wallof the hole being drilled serves to support the cutting means so thatthe latter advances through the tissue.
 2. The method of claim 1 whereinthe tissue is bone.
 3. The method of claim 1 wherein the tissue is softtissue.
 4. The method of claim 2 wherein said fibers are formed at thedistal end of the cable so as to themselves form said cutting means, andwherein said cable is rotated so that fibers at the distal end of thecable separate from each other so as to drill a hole in said bone of adiameter larger than the diameter of the cable adjacent but spaced fromits distal end.